JP2018142640A - Method for producing RTB-based sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an R-TB-based sintered magnet capable of further improving the holding force. SOLUTION: A step of preparing an R-TB-based sintered magnet and an RLRHM alloy (RL is Nd and / or Pr, RH is Dy and / or Tb,) on the surface of the R-TB-based sintered magnet. M is one or more selected from the group consisting of Al, Cu, Fe, Ga, Co, Ni, and Zn), and R- in a state where Al fluoride and / or Al oxide powder is present. It includes a step of performing heat treatment at a temperature equal to or lower than the sintering temperature of a TB-based sintered magnet. The RLRHM alloy contains RL + RH in an atomic ratio of 50 atomic% or more, M in an atomic ratio of 10 atomic% or more, and RL: RH = 96: 4 to 10:90, and has a melting point equal to or lower than the heat treatment temperature. The heat treatment is performed in a state where the RLRHM alloy powder and the Al fluoride and / or Al oxide powder are present on the surface of the sintered magnet at a mass ratio of RL: Al compound = 82: 18 to 75:25. .. [Selection diagram] None

Description

The present invention relates to a method for producing an R-T-B based sintered magnet (R is a rare earth element, T is Fe or Fe and Co, and B is boron) having an R ₂ T ₁₄ B type compound as a main phase.

  R-T-B system sintered magnets are known as the most powerful magnets among permanent magnets. Voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), industrial It is used in various motors such as equipment motors and home appliances.

The RTB-based sintered magnet is composed of a main phase mainly composed of an R ₂ T ₁₄ B compound and a grain boundary phase located at the grain boundary portion of the main phase. The main phase R ₂ T ₁₄ B compound has a high saturation magnetization and an anisotropic magnetic field, and forms the basis of the characteristics of the R—T—B system sintered magnet.

At a high temperature, the coercive force H _cJ (hereinafter sometimes simply referred to as “H _cJ ”) of the _RTB -based sintered magnet decreases, and irreversible thermal demagnetization occurs. Therefore, in particular, an _RTB -based sintered magnet used for an electric vehicle motor is required to have a high _HcJ .

In the RTB-based sintered magnet, a part of the light rare earth element RL (for example, Nd or Pr) contained in R in the R ₂ T ₁₄ B compound is a heavy rare earth element RH (for example, Dy or Tb). Substitution is known to improve _HcJ . As the substitution amount of RH increases, _HcJ improves.

However, when RL in the R ₂ T ₁₄ B compound is replaced with RH, the H _{cJ of the RTB} -based sintered magnet is improved, while the residual magnetic flux density B _r (hereinafter simply referred to as “B _r ”). There is). In particular, RH such as Tb and Dy has problems such as the supply is not stable and the price fluctuates greatly due to the small amount of resources and the limited production area. Yes. Therefore, in recent years, it has been demanded to improve _HcJ without using RH as much as possible.

On the other hand, so as not to reduce the B _r, to improve the H _cJ of the R-T-B based sintered magnets have been studied with less heavy rare-earth element RH. For example, fluoride or oxide of heavy rare earth element RH, or various metals M or M alloys, either individually or mixed, are present on the surface of the sintered magnet, and heat treatment is performed in that state, _thereby improving _HcJ . It has been proposed to diffuse the contributing heavy rare earth element RH into the magnet. For example, Patent Document 1 discloses a method in which powders of R oxide, R fluoride, and R oxyfluoride are brought into contact with the surface of an R-T-B system sintered magnet and subjected to heat treatment to diffuse them into the magnet. Is disclosed. Patent Document 2 discloses a method of performing diffusion heat treatment in a state where RLM alloy powder and RH fluoride powder are present on the surface of an R-T-B system sintered magnet.

International Publication No. 2006/043348 International Publication No. 2015/163397

The techniques described in Patent Documents 1 and 2 are very excellent in that _HcJ of an R-T-B system sintered magnet can be improved with a smaller amount of heavy rare earth element RH. The inventor analyzed these RTB-based sintered magnets by cross-sectional observation. As a result, heavy rare earth elements RH diffused only in the outer shell of the main phase at a depth of about 200 μm from the magnet surface, and a clean network was obtained. It had a structure. However, it was found that RH diffused to the central portion of the main phase near the surface of the magnet. _Previous studies have shown that RH diffused in the center of the main phase contributes little to the improvement of _HcJ . Therefore, if RH can be diffused only in the main phase outer shell portion in the magnet surface layer portion, further improvement in _HcJ can be expected with the same amount of RH.

Embodiment of this invention provides the manufacturing method of the _{RTB type | system |} group sintered magnet which can improve _HcJ more largely.

  In the exemplary embodiment, the manufacturing method of the RTB-based sintered magnet of the present disclosure includes an RTB-based sintered magnet (R is a rare earth element, T is Fe or Fe and Co, and B is boron. ) And an RLRHM alloy (RL is Nd and / or Pr, RH is Dy and / or Tb, M is Al, Cu, Fe, Ga, Co) on the surface of the RTB-based sintered magnet The RTB-based sintered magnet is sintered in a state where one or more powders selected from the group consisting of Ni, Zn, and Al fluoride and / or Al oxide powder are present. Heat treatment at a temperature lower than the temperature, wherein the RLRHM alloy has RL + RH of 50 atomic% or more of the whole RLRHM alloy, M is 10 atomic% or more of the whole RLRHM alloy, and RL and RH are RL: RH = 96: 4 In an atomic ratio of -10: 90, In addition, the melting point of the RLRHM alloy is equal to or lower than the temperature of the heat treatment, and the heat treatment is performed when the RLRHM alloy powder and the Al fluoride and / or Al oxide powder are RL: Al compound = 82: 18- The mass ratio is 75:25, and the R-T-B sintered magnet is present on the surface of the sintered magnet.

According to the embodiment of the present disclosure, the _HcJ of the _RTB -based sintered magnet can be improved.

It is a graph which shows the relationship between the compounding ratio of an Al compound, and _HcJ . It is a cross-section element mapping analysis photograph of the magnet surface of sample F3 *, and is an element mapping of SEM image, Nd, Cu, fluorine (F), Tb, and Al, respectively, from the upper left. It is a cross-sectional element mapping analysis photograph of the magnet surface of sample O3 *, and is an element mapping of SEM image, Nd, Cu, Tb, and Al, respectively from the upper left. (A) is a SEM image of a wider area than the SEM image of the sample F3 * in FIG. 2A, (b) is a SEM image of a wider area than the SEM image of the sample O3 * in FIG. 2B, and (c) is It is a cross-sectional SEM image of the magnet (comparative example) corresponding to the magnet of patent document 2 produced separately.

As a method of improving _HcJ by effectively using less RH, the present inventor has developed an RLRHM alloy, an Al fluoride and / or an Al oxide (hereinafter referred to as an Al compound) on the surface of an R-T-B system sintered magnet. It was found that _HcJ was specifically improved by heat treatment with a compounding ratio in a specific range. The obtained magnet was found to have a structure in which RH diffused deeper into the magnet than in the conventional example, and the main phase was clearly separated by a two-particle grain boundary. It was also found that the structure of the magnet surface layer portion formed by this method has a clean core-shell structure in which RH diffuses only in the main phase outer shell.

[Preparation of RTB-based sintered magnet base material]
An RTB-based sintered magnet base material to be diffused of the heavy rare earth element RH is prepared. In this specification, for the sake of easy understanding, an RTB-based sintered magnet that is an object of diffusion of the heavy rare earth element RH may be strictly referred to as an RTB-based sintered magnet base material. The term “RTB-based sintered magnet” includes such an “RTB-based sintered magnet base material”. As this RTB-based sintered magnet base material, a known material can be used, for example, having the following composition.
Rare earth element R: 12-17 atom%
B (a part of B (boron) may be substituted with C (carbon)): 5 to 8 atomic%
Additive element M ′ (selected from the group consisting of Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi At least one): 0 to 2 atomic%
T (a transition metal element mainly composed of Fe and may contain Co) and inevitable impurities: balance

  Here, the rare earth element R is mainly a light rare earth element RL (at least one element selected from Nd and Pr), but may contain a heavy rare earth element. In addition, when a heavy rare earth element is contained, it is preferable that at least one of Dy and Tb is included.

  The RTB-based sintered magnet base material having the above composition is manufactured by an arbitrary manufacturing method. The RTB-based sintered magnet base material may be sintered, or may be subjected to cutting or polishing.

[RLLRM alloy]
In the RLRHM alloy, RL is Nd and / or Pr, RH is Dy and / or Tb, M is one or more powders selected from the group consisting of Al, Cu, Fe, Ga, Co, Ni, and Zn. The RLRHM alloy contains RL + RH at 50 atomic% or more of the whole RLRHM alloy, M at 10 atomic% or more of the whole RLRHM alloy, and RL and RH in an atomic ratio of RL: RH = 96: 4 to 10:90. RL: RH is preferably 90:10 to 20:80. The melting point of the RLRHM alloy is below the temperature of the diffusion heat treatment.

  RL is Nd and / or Pr, which has a high effect of reducing the Al compound. M is one or more selected from the group consisting of Al, Cu, Fe, Ga, Co, Ni, and Zn, which lowers the melting point of the RLRHM alloy below the diffusion heat treatment temperature described below and does not adversely affect the magnet properties; To do.

The RLRHM alloy is considered to play both the role of a diffusing agent for supplying RH that diffuses in the magnet to improve _HcJ and the role of a reducing agent that reduces the Al compound. When RH: RH is less than 96: 4, that is, when RH is less than 4 atom% of RL + RH, RH sufficient to sufficiently improve _HcJ cannot be supplied. When RL: RH is on the side where RL is less than 10:90, that is, when RL is less than 10 atomic% of RL + RH, there is not enough power to reduce the Al compound. It is difficult to exhibit the effect of being present together with the RLRHM alloy.

  In order to sufficiently diffuse RH into the magnet and reduce the Al compound, the RLRHM alloy is preferably melted during the diffusion heat treatment. Therefore, the melting point of the RLRHM alloy is preferably equal to or lower than the temperature of the diffusion heat treatment. For that purpose, M may be 10 atomic% or more of the entire RLRHM alloy.

  Any method may be used for producing the RLRHM alloy, and examples thereof include a quenching method such as a roll quenching method and an atomizing method, and a method of pulverizing an RLRHM alloy ingot. The particle size of the RLRHM alloy powder is preferably 500 μm or less, more preferably 10 to 300 μm. In the present disclosure, the particle size of the powder is, for example, microscopic observation, a commercially available particle size distribution measuring device (for example, a laser diffraction / scattering particle size distribution measuring device manufactured by Microtrack Bell), JISZ8801 What is necessary is just to measure by classification etc. by the sieve described.

[Al compound]
As the Al compound, Al fluoride and / or Al oxide is used. Hereinafter, the entire Al fluoride and Al oxide are referred to as “Al compound”. Al is considered to diffuse into the magnet through the grain boundary together with RH. Any method may be used for producing the Al compound, and a commercially available Al compound can be used. The particle size of the Al compound is preferably 100 μm or less.

According to the study by the present inventors, the RLRHM alloy and the Al compound are present on the surface of the RTB-based sintered magnet so as to have a mass ratio of RL: Al compound = 82: 18 to 75:25. _HcJ specifically improves, RH diffuses deeper into the magnet than in the past, and has a structure in which the main phase is clearly separated by a two-particle grain boundary. The structure of the surface layer portion was found to have a clean core-shell structure in which RH diffused only in the main phase outer shell. When the compounding ratio of the Al compound is defined as the compounding ratio with respect to the RLRHM alloy (Al compound / (RLLRHM alloy + Al compound)), the preferable range of the compounding ratio is 8 to 12% by mass.

[Application]
Any method may be used in which the powder of the RLRHM alloy and the powder of the Al compound are present on the surface of the RTB-based sintered magnet. For example, a method in which RLRHM alloy powder and Al compound powder are dispersed on the surface of an R-T-B sintered magnet, and RLRHM alloy powder and Al compound powder are dispersed in a solvent such as pure water or an organic solvent. A method in which an RTB-based sintered magnet is dipped and pulled up, an RLRHM alloy powder and an Al compound powder are mixed with a binder or a solvent to produce a slurry, and this slurry is converted into an RTB A method of coating the surface of a sintered magnet, granulating a powder of an RLRHM alloy and an Al compound together with a binder to produce a granulated powder, and applying this granulated powder to the surface of an RTB-based sintered magnet Any of the methods of attaching to can be performed.

  If the binder and the solvent are substantially removed from the surface of the R-T-B system sintered magnet by thermal decomposition or evaporation at a temperature not higher than the melting point of the RLRHM alloy in the temperature raising process of the subsequent heat treatment, Well, not particularly limited. Examples of the binder include polyvinyl alcohol, ethyl cellulose, polyester and the like. The RLRHM alloy powder and the Al compound powder may be present on the surface of the RTB-based sintered magnet in a state where they are mixed, or may be present separately. In the method of the present disclosure, since the RLRHM alloy has a melting point lower than the heat treatment temperature, it melts during heat treatment, and the surface of the R-T-B system sintered magnet has reduced RH of R-T-B. It becomes easy to diffuse inside the sintered magnet. Therefore, before the RLRHM alloy powder and the Al compound powder are present on the surface of the R-T-B system sintered magnet, special cleaning such as pickling is performed on the surface of the R-T-B system sintered magnet. There is no need to perform the conversion process. Of course, it does not exclude performing such a cleaning process. Further, even if the surface of the RLRHM alloy powder particles is somewhat oxidized, there is almost no influence on the diffusion of RH and the effect of reducing the Al compound.

  The manufacturing method of the present disclosure does not necessarily exclude the presence of powder (third powder) other than the RLRHM alloy and Al compound powder on the surface of the R-T-B sintered magnet. Care must be taken not to inhibit diffusion of RH in the Al compound into the R-T-B system sintered magnet. The mass ratio of the powder of “RLLRHM alloy and Al compound” in the entire powder existing on the surface of the RTB-based sintered magnet is desirably 70% or more.

According to the manufacturing method of the present disclosure, it is possible to _efficiently improve the _HcJ of the _RTB -based sintered magnet with a small amount of RH. The amount of RH element in the powder present on the surface of the RTB-based sintered magnet is preferably 0.2 to 1.5 mass% with respect to the RTB-based sintered magnet.

[Diffusion heat treatment]
The heat treatment temperature for diffusion is not higher than the sintering temperature of the RTB-based sintered magnet (specifically, for example, 1000 ° C. or lower), and is higher than the melting point of the RLRHM alloy powder. Specifically, the heat treatment temperature is preferably 500 ° C. or higher as the temperature of the RTB-based sintered magnet. The heat treatment time is, for example, 10 minutes to 72 hours. Moreover, you may perform the heat processing for 10 minutes-72 hours at 400-700 degreeC as needed after the heat processing for diffusion.

(Experimental example 1)
First, by a known method, the composition ratio Nd = 13.4, B = 5.8, Al = 0.5, Cu = 0.1, Co = 1.1, and the balance = Fe (atomic%) RT -B system sintered magnet was produced. This was machined to obtain an R-T-B system sintered magnet base material of 4.9 mm × 7.4 mm × 7.4 mm. Magnetic properties of the obtained R-T-B based sintered magnet base material where a measured by B-H _{tracer, H cJ} is 1035kA / m, _{B r} was 1.45 T.

  As will be described later, the magnetic properties of the RTB-based sintered magnet after heat treatment are measured after removing the surface of the RTB-based sintered magnet by machining. For this reason, the surface of the R-T-B sintered magnet base material is also removed by machining by 0.1 mm in the direction of 4.9 mm and by 0.2 mm in the direction of 7.4 mm. The measurement was made after measuring the size of 4.7 mm × 7.0 mm × 7.0 mm. Moreover, when the impurity amount of the R-T-B system sintered magnet base material was separately measured with a gas analyzer, oxygen was 810 ppm, nitrogen was 370 ppm, and carbon was 870 ppm.

Next, an alloy having a composition of Nd ₅₇ Tb ₁₃ Cu ₃₀ (atomic%) (melting point: 570 ° C.) was prepared. This alloy is a powder having a particle size of 106 μm or less prepared by an atomizing method. The obtained alloy powder was mixed with AlF ₃ powder having a particle size of 20 μm or less and Al ₂ O ₃ powder having a particle size of 20 μm or less at a blending ratio (Al compound / (Nd ₅₇ Tb ₁₃ Cu ₃₀ + Al compound)) shown in Table 1. A mixed powder was obtained. This mixed powder was mixed with polyvinyl alcohol and water to obtain a slurry. This slurry is placed on one surface of an R-T-B system sintered magnet base material of 7.4 mm × 7, 4 mm and the amount of RH (Tb) is 0.5 mass relative to the R-T-B system magnet base material. % Was applied and dried.

  The Mo plate on which this RTB-based sintered magnet base material was placed was accommodated in a processing container and covered. This lid does not prevent the gas from entering or leaving the container. This was accommodated in a heat treatment furnace and heat-treated at 900 ° C. for 10 hours in an Ar atmosphere of 100 Pa. The heat treatment was carried out under the above conditions after the temperature was raised while evacuating from room temperature and the atmospheric pressure and temperature reached the above conditions. Then, after the temperature was lowered to room temperature, the Mo plate was taken out and the RTB-based sintered magnet was collected. The recovered RTB-based sintered magnet was returned to the processing vessel and accommodated again in a heat treatment furnace, and heat treatment was performed at 490 ° C. for 3 hours in a vacuum of 10 Pa or less. This heat treatment was also performed under the above conditions after the temperature was raised while evacuating from room temperature and the atmospheric pressure and temperature reached the above conditions. Thereafter, the temperature was lowered to room temperature, and then the R-T-B sintered magnet was collected.

The surface of the obtained RTB-based sintered magnet was polished and removed by machining by 0.1 mm in the direction of 4.9 mm and by 0.2 mm in the direction of 7.4 mm, respectively, and 4.7 mm × 7. Samples F1 to O5 of 0 mm × 7.0 mm were obtained. Magnetic characteristics of the obtained sample F1~O5 measured by the B-H tracer _was determined _{H cJ} and _{B r.} The results are shown in Table 1. Moreover, the relationship between the compounding ratio of an Al compound and _HcJ is shown in FIG. Sample 1 is a sample that was heat-treated with Nd ₅₇ Tb ₁₃ Cu ₃₀ present on the surface of the magnet without blending an Al compound. In Table 1, “Nd: Al compound” indicates the mass ratio of RL (Nd in this experimental example): Al compound, and ΔH _cJ indicates the difference from H _cJ of the R-T-B system sintered magnet base material. , .DELTA.B _r represents the difference between the _{B r} of the R-T-B based sintered magnet base material.

From FIG. 1, it was found that when the compounding ratio of the Al compound was 8 to 12% by mass (Nd: Al compound was 82:18 to 75:25 by mass ratio), _HcJ was specifically improved. In particular, it can be seen that a remarkably high _HcJ was achieved when the compounding ratio of the Al compound was 9.1 to 10.7% by mass.

  Further, a cross-sectional element mapping analysis immediately below the magnet surface was performed on samples that were prepared in the same manner as Samples F3 and O3 and were not machined after heat treatment (hereinafter referred to as Samples F3 * and O3 *). FIG. 2A is a cross-sectional elemental mapping analysis photograph of the magnet surface of sample F3 *, which is an elemental mapping of an SEM image, Nd, Cu, fluorine (F), Tb, and Al, respectively, from the upper left. FIG. 2B is a cross-sectional elemental mapping analysis photograph of the magnet surface of sample O3 *, which is an elemental mapping of the SEM image, Nd, Cu, Tb, and Al, respectively, from the upper left.

  As can be seen from FIGS. 2A and 2B, Tb diffused only in the outer shell portion of the main phase even near the magnet surface, and a clean core-shell structure was observed. Al is recognized as diffusing through the grain boundary in the same manner as Tb, but it has diffused into the main phase as compared with Tb. Furthermore, according to a wide area mapping analysis, it was observed that Tb was sufficiently diffused deeper than 500 μm of the magnet.

  FIG. 3A is an SEM image of a wider area than the SEM image of the sample F3 * in FIG. 2A. FIG. 3B is an SEM image of a wider area than the SEM image of the sample O3 * in FIG. 2B. FIG. 3C is a cross-sectional SEM image of a magnet (comparative example) corresponding to the magnet described in Patent Document 2 that is separately manufactured.

As can be seen from FIG. 3, in the example of the present invention, it is observed that the main phase is clearly divided by a clear grain boundary structure as compared with the comparative example. The _{reason why the HcJ} of the magnet in the embodiment of the present invention is specifically improved depending on the compounding ratio of the Al compound is that of the embodiment of the present invention as shown in FIG. 2A, FIG. 2B, and FIG. It is considered that the characteristics of the structure of the magnet have an effect.

The method for producing an RTB-based sintered magnet according to the present invention can provide an _RTB -based sintered magnet in which _HcJ is improved by a smaller amount of heavy rare earth element RH.

Claims (1)

Preparing a R-T-B sintered magnet (R is a rare earth element, T is Fe or Fe and Co, and B is boron);
An RLRHM alloy (RL is Nd and / or Pr, RH is Dy and / or Tb, M is Al, Cu, Fe, Ga, Co, Ni, Zn on the surface of the RTB-based sintered magnet) Heat treatment at a temperature equal to or lower than the sintering temperature of the RTB-based sintered magnet in the presence of Al fluoride and / or Al oxide powder. When,
Including
The RLRHM alloy includes RL + RH at 50 atomic% or more of the entire RLRHM alloy, M includes 10 atomic% or more of the entire RLRHM alloy, and RL and RH in an atomic ratio of RL: RH = 96: 4 to 10:90, and The melting point of the RLRHM alloy is equal to or lower than the temperature of the heat treatment,
In the heat treatment, the RLRHM alloy powder and the Al fluoride and / or Al oxide powder are sintered at the mass ratio of RL: Al compound = 82: 18 to 75:25. The manufacturing method of the RTB type | system | group sintered magnet performed in the state which exists in the said surface of a magnet.